Security devices, such as padlocks and other types of conventional locks, are used, for example, to prevent access to a room, building, enclosure, container, or piece of equipment. Exemplary padlocks include those opened by a key and those opened by manipulation of lock components in accordance with a unique combination. In a conventional padlock, a shackle is secured within a lock body by one or more internal locking members that are received in corresponding notches in the shackle to prevent axial withdrawal of the shackle from the lock body. Certain conventional padlocks of this type may be susceptible to unauthorized opening by manipulation of the locking members using a lock-picking tool or other instrument inserted into the lock body (e.g., through the shackle holes) to disengage the locking members from the shackle notches.